Homeowners install concrete in a variety of places in and around their homes, including patios, garages, walls and walkways. Using a grill or outdoor fire pit on concrete or too close to a concrete wall can result in burn marks on the surface. Accidental fires also leave black burn marks on concrete. Heat from the fire does not destroy the structural integrity of the concrete, but it does detract from its beauty. Several cleaning methods effectively clean burn marks off concrete. Begin with the mildest solution and progress to stronger solutions until the burn marks are no longer visible.
Attach a high-pressure nozzle to a garden hose. Direct the stream of water at the burn marks to wash the soot from the surface.
Pour cola over the burn mark. Let the cola sit on the surface for 10 to 15 minutes. Rinse the cola from the concrete. Repeat two to three times to lighten or remove the burn mark entirely.
Add 1 gallon of hot water to a bucket and pour in 3/4 cup of powdered dishwasher detergent. Submerge a stiff-bristle scrub in the bucket. Scrub burn marks beginning at the outer edge of the mark, working toward the centre. Rinse the burn mark well with clear water.
Wet the burn mark with clear water. Add a layer of oxygenated bleach over the wet burn mark. Rub the oxygenated bleach into the concrete with a scrub brush. Let the oxygenated bleach remain on the burn mark for 20 to 30 minutes. Rinse the oxygenated bleach residue off the concrete with clear water.
Spray the burn mark with clear water. Sprinkle a generous layer of a bleach-based scouring powder over the burn mark. Wet a stiff-bristle scrub brush with water and scrub the area. Let the scouring powder remain on the surface for 10 to 15 minutes. Scrub the burn mark with a scrub brush a second time. Rinse the scouring powder residue from the concrete surface with clear water. Repeat two to three times or until the burn mark disappears.
Wet the burn mark with clear water and squirt liquid dish soap onto the stain. Rub the stain with a scrub brush to create suds. Sprinkle a generous layer of ground pumice over the burn mark. Rub the pumice into the soap-covered burn mark vigorously with a scrub brush. Continue to scrub the burn mark until the stain disappears. Rinse the area with clear water.
Spray the burn mark with oven cleaner. Allow the cleaner to remain on the burn marks for 45 to 60 minutes. Scrub the burn marks with a stiff-bristle scrub brush until the stain is no longer visible. Rinse the concrete thoroughly with clear water.
Put on acid-approved safety goggles, rubber gloves, rubber boots and an acid-approved respirator. Mix one part muriatic acid with six parts water to create a weak muriatic acid cleaning solution. Slowly pour the muriatic acid mixture over the burn mark. Let the acid stand on the concrete burn mark for five to 10 minutes. Rinse the area very well with clear water.
Wear gloves and eye protection when cleaning burn marks on concrete. Clean burn marks as soon as possible.
Use extreme care when handling muriatic acid, as it is highly corrosive and damaging to the skin.